Distribution and morphological changes of the Golgi apparatus during Drosophila spermatogenesis

Genome-wide 5'-C-phosphate-G-3' methylation patterns reveal the effect of heat stress on the altered semen quality in Bubalus bubalis

Semen production and quality are closely correlated with different environmental factors in bovines, particularly for the buffalo (Bubalus bubalis) bulls reared under tropical and sub-tropical conditions. Factors including DNA methylation patterns, an intricate process in sperm cells, have an impact on the production of quality semen in buffalo bulls under abiotic stress conditions. The present study was conducted to identify DNA methylome signatures for semen quality in Murrah buffalo bulls, acclaimed as a major dairy breed globally, under summer heat stress. Based on semen quality parameters that significantly varied between the two groups over the seasons, the breeding bulls were classified into seasonally affected (SA = 6) and seasonally non-affected (SNA = 6) categories. DNA was isolated from purified sperm cells and sequenced using the RRBS (Reduced Representation Bisulfite Sequencing) technique for genome-wide methylome data generation. During the hot summer months, the physiological parameters such as scrotal surface temperature, rectal temperature, and respiration rate for both the SA and SNA bulls were significantly higher in the afternoon than in the morning. Whereas, the global CpG% of SA bulls was positively correlated with the afternoon's scrotal surface and rectal temperature. The RRBS results conveyed differentially methylated cytosines in the promoter region of the genes encoding the channels responsible for Ca2+ exchange, NPTN, Ca2+ activated chloride channels, ANO1, and a few structure-related units such as septins (SEPT4 and SEPT6), SPATA, etc. Additionally, the hypermethylated set of genes in SA was significantly enriched for pathways such as the FOXO signaling pathway and oocyte meiosis. The methylation patterns suggest promoter methylation in the genes regulating the sperm structure as well as surface transporters, which could contribute to the reduced semen quality in the Murrah buffalo bulls during the season-related heat stress.

The Organization of the Golgi Structures during Drosophila Male Meiosis Requires the Citrate Lyase ATPCL

During spermatogenesis, the Golgi apparatus serves important roles including the formation of the acrosome, which is a sperm-specific organelle essential for fertilization. We have previously demonstrated that D. melanogaster ATP-dependent Citrate Lyase (ATPCL) is required for spindle organization, cytokinesis, and fusome assembly during male meiosis, mainly due to is activity on fatty acid biosynthesis. Here, we show that depletion of DmATPCL also affects the organization of acrosome and suggest a role for this enzyme in the assembly of Golgi-derived structures during Drosophila spermatogenesis.

Formation of the acrosome complex in the bush cricket Gampsocleis gratiosa (Orthoptera: Tettigoniidae)

The acrosome complex plays an indispensable role in the normal function of mature spermatozoa. However, the dynamic process of acrosome complex formation in insect remains poorly understood. Gampsocleis gratiosa Brunner von Wattenwyl possesses the typical characteristic of insect sperms, which is tractable in terms of size, and therefore was selected for the acrosome formation study in this report. The results show that acrosome formation can be divided into six phases: round, rotating, rhombic, cylindrical, transforming and mature phase, based on the morphological dynamics of acrosome complex and nucleus. In addition, the cytoskeleton plays a critical role in the process of acrosome formation. The results from this study indicate that: (1) glycoprotein is the major component of the acrosome proper; (2) the microfilament is one element of the acrosome complex, and may mediate the morphologic change of the acrosome complex; (3) the microtubules might also shape the nucleus and acrosome complex during the acrosome formation.

The role of acroblast formation during Drosophila spermatogenesis

Protein recycling is important for maintaining homeostasis of the Golgi and its cisternae. The Vps54 (Scat) protein, a subunit of the GARP tethering complex, is a central factor in retrograde transport to the trans-Golgi. We found the scat¹ mutant to be male sterile in Drosophila with individualization problems occurring during spermatogenesis. Another typically observed phenotype was the abnormal nuclear structure in elongated mutant cysts. When examining the structure and function of the Golgi, a failure in acrosome formation and endosome-Golgi vesicular transport were found in the scat¹ mutant. This acrosome formation defect was due to a fault in the trans-Golgi side of the acroblast ribbon. When testing a mutation in a second retrograde transport protein, Fws, a subunit of the conserved oligomeric Golgi (COG) tethering complex, the acroblast structure, was again disrupted. fws^P caused a similar, albeit milder, acrosome and sperm individualization phenotype as the scat¹ mutant. In the case of fws^P the cis side of the acroblast ribbon was dispersed, in-line with the intra-Golgi retrograde function of COG. Our results highlight the importance of an intact acroblast for acrosome formation, nuclear elongation and therefore sperm maturation. Moreover, these results suggest the importance of retrograde tethering complexes in the formation of a functional Golgi ribbon.

Summary: This study demonstrates that retrograde tethering complexes are necessary to form a functional acroblast, which is essential for normal nuclear elongation and acrosome formation during Drosophila spermatogenesis.

Myt1 inhibition of Cyclin A/Cdk1 is essential for fusome integrity and premeiotic centriole engagement in Drosophila spermatocytes

Drosophila Myt1 is essential for male fertility. Loss of Myt1 activity causes defective fusomes and premature centriole disengagement during premeiotic G2 phase due to lack of Myt1 inhibition of Cyclin A/Cdk1. These functions are distinct from known roles for Myt1 inhibition of Cyclin B/Cdk1 used to regulate G2/MI timing.

Regulation of cell cycle arrest in premeiotic G2 phase coordinates germ cell maturation and meiotic cell division with hormonal and developmental signals by mechanisms that control Cyclin B synthesis and inhibitory phosphorylation of the M-phase kinase, Cdk1. In this study, we investigated how inhibitory phosphorylation of Cdk1 by Myt1 kinase regulates premeiotic G2 phase of Drosophila male meiosis. Immature spermatocytes lacking Myt1 activity exhibit two distinct defects: disrupted intercellular bridges (fusomes) and premature centriole disengagement. As a result, the myt1 mutant spermatocytes enter meiosis with multipolar spindles. These myt1 defects can be suppressed by depletion of Cyclin A activity or ectopic expression of Wee1 (a partially redundant Cdk1 inhibitory kinase) and phenocopied by expression of a Cdk1F mutant defective for inhibitory phosphorylation. We therefore conclude that Myt1 inhibition of Cyclin A/Cdk1 is essential for normal fusome behavior and centriole engagement during premeiotic G2 arrest of Drosophila male meiosis. The novel meiotic functions we discovered for Myt1 kinase are spatially and temporally distinct from previously described functions of Myt1 as an inhibitor of Cyclin B/Cdk1 to regulate G2/MI timing.